1. Field of the Invention
This invention relates to an improved process to make a novel form of a alpha alumina monohydrate powder useful as a shear-rate thinning material in drilling fluids.
2. Description of the Previously Published Art
U.S. Pat. No. 4,240,915 to Block describes water-based, clay-free drilling fluids for use in drilling bore holes into subterranean formations which contain water, a water-loss inhibitor, a weighting agent and aluminum hydroxide as a viscosifying agent. The aluminum hydroxide viscosifying agent is prepared in an aqueous medium by contacting and mixing under a high degree of agitation an acid reactant and a base reactant wherein at least one of the acid or base reactants contains aluminum. The acidic reactant can be either an inorganic acid or a salt of a strong acid and a weak base. These aqueous compositions contain a significant amount of water and are expensive to transport.
To reduce the water weight, attempts have been made to dry the aluminum hydroxide. However, when it is dried, the aluminum hydroxide powder does not readily disperse back into water to yield the original shear-rate thinning material. Thus this dried form would not be suitable for its intended use at a well site where it should be able to disperse in water to form a shear-rate thinning drilling fluid.
U.S. Pat. No. 4,244,835 to Block describes one way to solve this problem of redispersing the dried aluminum hydroxide powder in water. There it was necessary to add a base such as a water soluble alkali metal hydroxide, carbonate or oxide to the mixture and it was further necessary to employ high shear mixing. This technique, however, not only requires the presence of additional chemicals which increase the cost of the drilling fluid but it also requires high shear mixing. In addition the handling of the caustic is hazardous and it may result in the pH of the reaction mixture being too high which would then require readjusting with an acidic material.
3. Objects of the Invention
It is an object of this invention to produce a solid alpha alumina monohydrate powder which can readily be dispersed in water to yield a highly shear-rate thinning fluid without the aid of large quantities of acids, bases or excessive high shear mixing.
It is an object of this invention to produce a dried alpha alumina monohydrate powder containing an aluminum compound which when expressed as AlO(OH) is at least about 10% by weight. Such a dried powder can be readily dispersed in water to yield a highly shear-rate thinning fluid with an n value in the power law model to be discussed below of less than 0.3 without the aid of large quantities of acids, bases or excessive high shear mixing.
It is a further object of this invention to form a shear-rate thinning alpha alumina monohydrate in an aqueous system by reacting under a high degree of agitation an acid reactant and a base reactant wherein at least one of the acid or base reactants contains aluminum and to then utilize a special thermal treatment to produce a unique alpha alumina monohydrate form of aluminum hydroxide which can be subsequently dried to a low water content and then easily redispersed in water to form a shear-rate thinning material without the need for any large quantities of auxiliary dispersing agents or any expensive high shear mixing equipment.
It is a further object of this invention to produce an aluminum hydroxide viscosifying material which can be dried to a greater extent than ordinarily produced alpha alumina monohydrate.
These and further objects will become apparent as the description of the invention proceeds.